(1) Field of the Invention
The present invention relates to a low-pressure mercury vapor discharge lamp provided with a globe housing an arc tube therein, and to a manufacturing method therefore. Especially, the present invention relates to a bulb-type fluorescent lamp.
(2) Description of the Related Art
A bulb-type fluorescent lamp, which is one type of a low-pressure mercury vapor discharge lamp, has higher luminance efficacy and a longer life in comparison with a filament lamp. Due to these advantages, a bulb type fluorescent lamp is recognized as an energy-saving lighting apparatus, and thus rapidly becoming prevalent.
FIG. 1 shows a partly-broken, vertical sectional view showing the construction of a conventional bulb-type fluorescent lamp. As shown in the figure, the bulb-type fluorescent lamp 51 is composed of a serpentine arc tube 53, a holder 54 for holding the arc tube 53, a lighting circuit 57 being arranged on the opposite side of the holder 54 to the arc tube 53, a case 55 for housing the lighting circuit 57 therein, and a globe 52 mounted to the case 55 in a manner to cover the arc tube 53 therein.
As shown in FIG. 2, an open end portion 52a of the globe 52 is loosely inserted into an open end portion 55a of the case 55. The globe 52 is fixed to the case 55 with the adhesive 56 that is supplied entirely along the inner periphery of the open end portion 55a of the case 55. Here, the adhesive 56 is supplied through a single supply nozzle to the open end portion 55a. To be more specific, while the adhesive 56 is supplied through the supply nozzle that is fixed at one location, the case 55 is rotated one full turn in the circumferential direction. With this arrangement, the adhesive 56 is supplied entirely along the inner periphery of the open end portion 55a of the case 55.
The conventional bulb-type fluorescent lamp 51, however, has the following problem: That is, heat generated by the arc tube 53 during light emission is conducted to the case 55 through the adhesive 56 supplied along the entire periphery of the open end portion 52a of the globe 52. As a result, the surrounding temperature of the lighting circuit 57 housed in the case 55 rises significantly. Being exposed to such a high temperature, components constituting the lighting circuit 57 become less reliable, if not damaged.
Another problem lies in the manufacturing method. In the conventional method, the case 55 must be rotated one full turn in order to supply the adhesive 56 entirely along the inner periphery of the open end portion 55a. Such a supplying process is time consuming, and thus undesirably reduces productivity in manufacturing such fluorescent lamps.